A two dimensional memory device has a storage capacity that depends on the restrictions in the manufacturing process thereof, such as the resolution limit of photolithography. In order to overcome this limitation, a three-dimensional memory device has been under development, which comprises memory cells disposed along semiconductor channels extending in a direction perpendicular to a substrate. In such a memory device, however, a variation of electric resistance between the memory cells and a source interconnect sometimes causes a channel current flowing through the memory cells to change, resulting in the deterioration of performance such as accuracy of data readout. Hence, there is a demand for suppressing the variation of the channel current.